1. Field of the Invention
The present invention relates to a method and apparatus for controlling printing in a thermal printer. More specifically, the present invention relates to a method and apparatus for controlling printing in a thermal printer while maintaining a temperature of a thermal printhead (TPH) for applying a predetermined heat to a double-sided thermal reactive paper.
2. Description of the Related Art
Thermal printers include a number of devices which typically use print paper (hereinafter, referred to as “thermal reactive paper”) which displays a predetermined color by reacting to heat, and include a number of devices which typically use an ink ribbon which transfers a predetermined color to the paper by reacting to heat for printing. The devices using the ink ribbon require an additional apparatus for driving the ink ribbon so that the structure thereof is complicated and a final product is expensive. Also, since the ink ribbon is provided as a consumable product, it needs to be continuously replaced, such that resulting printing costs per page are high.
FIG. 1 is a sectional view of a typical thermal reactive paper. Referring to FIG. 1, a thermal reactive paper 10 has ink layers 12 and 13 of a predetermined color formed on first and second surfaces of a base sheet 11, respectively. Each of the ink layers 12 and 13 may have a monolayer structure comprised of a single color ink, or a multilayered structure for the display of two or more colors. For example, the ink layer 12 on the first surface of the base sheet 11 may have two layers for the display of magenta (M) and cyan (C) colors, while the ink layer 13 on the second surface may have a single layer for the display of a yellow (Y) color. The base sheet 11 is a transparent material. Additional details of thermal reactive paper are disclosed in U.S. Patent Application Publication No. 2003-0125206 of Bhatt et al., entitled “Thermal Imaging System”, the entire disclosure of which is incorporated herein by reference.
A thermal printer using the thermal reactive paper 10 typically comprises a thermal printhead (TPH) where a plurality of heating elements are arranged at a predetermined resolution in a widthwise direction of the thermal reactive paper 10. After printing is performed with respect to both sides of the thermal reactive paper 10, a color image appears on the thermal reactive paper as viewed from one side of the thermal reactive paper 10.
The quality of a color image of the thermal printer is greatly dependent on the temperature of the TPH, such that the temperature of the TPH should be maintained at a substantially constant value during printing. In particular, when the printer is in a ready mode or prints the first page, if the temperature of the TPH is lower than the minimum target temperature, the color of the ink layer of the thermal reactive paper is insufficiently displayed. Thus, spots may be formed on the thermal reactive paper.
To make the temperature of the TPH reach a value that is greater than the temperature of the minimum target temperature, the TPH needs to be preheated. Japanese Patent Laid-open No. 1996-25679, the entire disclosure of which is incorporated herein by reference, discloses a structure to increase the temperature of a printhead by installing a generating device and a temperature sensor at a support portion for supporting the heating elements and heating the generating device according to the temperature of the printhead. Japanese Patent Laid-open No. 2004-142357, the entire disclosure of which is incorporated herein by reference, further discloses a structure including a printhead, a temperature sensor, a cooling fan, and a heater to constantly maintain the temperature of the TPH.
However, a need remains for a system and method for effectively and efficiently controlling printing such that the temperature of a printhead of a thermal printer is maintained in a particular range.